1. Field of the Invention
The invention relates to polyurethanes and the production thereof and more particularly relates to polyurethanes using monocarboxylic acid salts of amines which contain ether and hydroxyl moieties as catalysts.
2. Description of the Prior Art
The use of a catalyst in preparing polyurethanes by the reaction of a polyisocyanate, a polyol and perhaps other ingredients is known. The catalyst is employed to promote at least two, and sometimes three major reactions that must proceed simultaneously and competitively at balanced rates during the process in order to provide polyurethanes with the desired physical characteristics. One reaction is a chain extending isocyanate-hydroxyl reaction by which a hydroxyl-containing molecule is reacted with an isocyanate-containing molecule to form a urethane. This increases the viscosity of the mixture and provides a polyurethane containing a secondary nitrogen atom in the urethane groups. A second reaction is a crosslinking isocyanate urethane reaction by which an isocyanate-containing molecule reacts with a urethane group containing a secondary nitrogen atom. The third reaction which may be involved is an isocyanate-water reaction by which an isocyanate-terminated molecule is extended and by which carbon dioxide is generated to blow or assist in the blowing of the foam. The third reaction is not essential if an extraneous blowing agent, such as a halogenated, normally liquid hydrocarbon, carbon dioxide, etc. is employed, but is essential if all or even a part of the gas for foam generation is to be generated by this in situ reaction (e.g. in the preparation of "one-shot" flexible polyurethane foams).
The reactions must proceed simultaneously at optimum balanced rates relative to each other in order to obtain a good foam structure. If carbon dioxide evolution is too rapid in comparison with chain extension, the foam will collapse. If the chain extension is too rapid in comparison with carbon dioxide evolution, foam rise will be restricted, resulting in a high density foam with a high percentage of poorly defined cells. The foam will not be stable in the absence of adequate crosslinking.
It has long been known that tertiary amines, such as trimethylamine, triethylamine, etc., are effective for catalyzing the second crosslinking reaction. Other typical tertiary amines are set forth in U.S. Pat. Nos. 3,925,368; 3,127,436; and 3,243,387 and German OLS Nos. 2,354,952 and 2,259,980. Some of the tertiary amines are effective for catalyzing the third water-isocyanate reaction for carbon dioxide evolution. However, tertiary amines are only partially effective as catalysts for the first chain extension reaction. To overcome this problem, the so-called "prepolymer" technique has been developed wherein a hydroxy-containing polyol component is partially reacted with the isocyanate component in order to obtain a liquid prepolymer containing free isocyanate groups. This prepolymer is then reacted with additional polyol in the presence of a tertiary amine to provide a foam. This method is still commonly employed in preparing rigid urethane foams, but has proven less satisfactory for the production of flexible urethane foams.
For flexible foams, a one-step or "one-shot" process has been developed wherein a tertiary amine, such as triethylenediamine, is employed in conjunction with an organic tin compound. Triethylenediamine is particularly active for promoting the water-isocyanate reaction and the tin compound is particularly active in synergistic combination with the triethylenediamine for promoting the chain extension reaction. However, even here, the results obtained leave much to be desired. Triethylenediamine is a solid and must be dissolved prior to use to avoid processing difficulties. Also, triethylenediamine and other of the prior art amines can impart a strong amine odor to the polyurethane foam.
The prior art section of U.S. Pat. No. 4,338,408 describes other polyurethane catalysts and their deficiencies and is incorporated by reference herein. Many of these problems were solved by the bis(aminoethyl)ether derivatives of U.S. Pat. No. 4,338,408, and it is the monocarboxylic acid salts of these derivatives which are the focus of the instant disclosure.
Generally, the use of amine salts as catalysts for the production of polyurethanes is well known. Usually, the amount of acid added to the basic amine catalyst is not enough to totally neutralize it (which would greatly inhibit its catalytic activity). The result is a "delayed action" catalyst; that is, a polyurethane tertiary amine catalyst not quite as active as the original amine which formed the salt in the first place but which nevertheless allows the polyurethane reaction to proceed smoothly, rapidly and efficiently.
U.S. Pat. No. 2,932,621 teaches the preparation of polyurethane foam utilizing a salt of dimethylethanolamine and a dicarboxylic acid (such as oxalic acid) as the catalyst. Triethylenediamine (TEDA) diformate salt may be employed in combination with an amount of 1-(2-hydroxypropyl) imidazole (not greater than the amount of the salt) as a catalyst to permit wider latitude in the organic tin catalyst in preparing polyurethane foams, accordin.g to U.S. Pat. No. 3,728,291.
U.S. Pat. Nos. 3,862,150 and 4,165,412 involve similar salts of tertiary amines and alpha-substituted carboxylic acids as delayed action catalysts in preparing polyurethanes and epoxy resins. The acid must have a carboxylic acid group in one end of the molecule and a decomposition promoting group selected from CN, SO, SO.sub.2, CO, NO.sub.2, COCH.sub.3 and CO-phenyl on the other end. An example is the salt of TEDA and cyanoacetic acid. Other typical amines mentioned are dimethylethanolamine and 2,2'-oxybis-dimethylethylamine.
Tertiary amino acid and tertiary amino acid-nitrile compositions have been found to be effective delayed action catalysts for polyurethane synthesis according to U.S. Pat. No. 4,086,213. These compounds, also referred to as salts, are to be used in combination with an organometallic catalyst, such as an organotin compound. The materials described in this patent are the reaction product of a primary or secondary amine, an aldehyde and a disubstituted acid; that is, a compound containing a carboxylic acid or nitrile group.
U.S. Pat. No. 4,115,634 teaches further that amine salts of amino acids are also good delayed action catalysts for organometallic catalyzed urethane synthesis. The acid which provides the basis for the salt is made by reacting an amine with an unsaturated acid, or with formaldehyde and hydrogen cyanide followed by hydrolysis of the resulting nitrile. A similar technique involving other amine salts of tertiary amino acids is revealed in U.S. Pat. No. 4,204,062. Here the salts are formed by initially reacting a primary or secondary amine with an aldehyde and a di-substituted acid to form a Mannich adduct and then reacting the resulting Mannich acid adduct with an amine.
Partial neutralization of tertiary amine catalysts such as per-methyl-tetraethylene pentamine and the like by aliphatic carboxylic acids, and subsequent use as catalysts in polyisocyanate addition processes, is apparently described in West German Offenlegungsschrift No. 2,812,256 (and European Pat. No. 4309) as abstracted in Derwent German Patents Abstracts, Week B40.
As can be seen from these brief descriptions, many of these amine salt catalysts are prepared by processes much too complicated to allow them to be useful and result in delayed action catalysts. There is a continuing need for polyurethane catalysts which are easily prepared and which give excellent reaction characteristics.